Figure 3. Soil biological activity vs. redox state (rH2). The
colors represent OM concentration and the shape is the treatment vs.
control group.
Redox potential tracked changes in soil management (Figure 2; Eh -20 mV
p = 0.048*), but the difference between management practices in
CO2burst was not significant (increase of 8 mg-C/kg, p =
0.06). CO2 burst is considered as an intermediate
indicator, changing over a period of a few years (Weil and Brady, 2016).
In this test, three years was not enough to result in a detectable
difference in CO2burst. It may be, that the
CO2 burst integrates more variables (Barnard et al.,
2020) than the redox and that some variables have developed in opposite
directions, confounding the effect of management. However,
CO2burst was found to correlate with texture but not
with structure, while redox correlated with both texture and structure
(Table 1), suggesting that redox can integrate soil properties that
change very rapidly, such as structure (Weil and Brady, 2016).
Soil structure had a marked effect on the redox potential (Figure 4)
(VESS vs. rH2, R2=0.35, p=0.04). In soils with good
structure (VESS < 2.75) the redox status was more oxidized
(rH2 30.5) compared to soils with poor structure (VESS
>3.25; rH2 28.6) (Figure 4). Even in poor
structure soils, most soils were classified as oxidized, indicating that
redox cannot be used as a replacement for the soil structure evaluation,
but that good structure is often found together with oxidized soils. OM
correlated with VESS (R2=0.42): soils with high OM
were often classified as having a good structure (Figure 4).